Self-releasing form for casting concrete slabs



p 7, 1965 w. L. JACKSON 3,204,316

SELF-RELEASING FORM FOR CASTING CONCRETE SLABS Filed Oct. 5, 1962 2 Sheets-Sheet 1 INVENTO'. WALTER L JAC N "W MW ATTORNEY P 1965 w. L. JACKSON 3,204,316

SELF'RELEASING FORM FOR CASTING CONCRETE SLABS Filed Oct. 5, 1962 2 Sheets-Sheet 2 FIG.3.

INVENTOR. WALTER L. JACKSON AT TORNE Y United States Patent 3,204,316 SELF-RELEASING FORM FUR CASTING CGNQRETE SLAES Walter L. Jackson, Richmond, Ind, assignor to Rex (:hainbelt Inc., a corporation of Wisconsin Filed Oct. 5, 15 62, Ser. No. 228,517 Claims. (Cl. 25-121) This invention relates generally to the art of casting monolithic concrete structural members of the type used in building construction and the like and more particularly to improved apparatus for molding precast flat floor slabs.

In one type of building construction, floors and ceilings are formed from precast flat slabs of concrete laid side by side with their ends resting on spaced supports to constitute a prefabricated spanning structure. Each precast slab is formed along each side with an indented keyway groove so arranged that when the slabs are laid in contiguous relationship the complementary side grooves form keyways or channels closed at the bottom and open at the top between the adjacent slabs. After the slabs are laid in position, the keyways or grout canals between them are filled with grout in plastic condition. The grout keys when hardened interlock the adjacent slabs in manner to form in effect a continuous unitary concrete platform that constitutes the ceiling of one room and the floor of the room above.

Monolithic flat floor slabs of this type are usually cast in a manufacturing yard or like establishment and transported in finished condition to the building site. The slabs are ordinarily molded by pouring freshly mixed concrete into forms of the required shape usually made of steel and containing reinforcing elements and other accessories. Because of the fact that the keyway grooves are indented into the sides of the slab it is not possible to with-draw a cast slab from a form without distorting or dismantling the form to some extent. Ordinarily the side pieces of the form which carry the elements that mold the indented grooves are made detachable and are disconnected from the bottom part of the form in order to release the slab for removal. This requires that the side pieces be detached by hand through unscrewing bolts or driving out Wedges or the like by the use of wrenches and hammers and that the separate loose parts must then be cleaned and reassembled in preparing the form for a subsequent casting operation. Furthermore, the joints or seals between the separate side pieces and the bottom part of the form are not tight enough to prevent leakage of fluid material from the concrete. This grout leakage may result in leaving exposed aggregates on the ceiling side of the finished slab and also may form protruding rough flanges on the slab. Such imperfections in the product must be repaired by hand finishing before the slab is marketed.

It is accordingly a general object of the present invention to provide an improved arrangement for casting monolithic concrete slabs.

Another object of the invention is to provide an improved slab casting form in which the side form elements are pivotally mounted to provide for outward swinging movement for releasing the cast slab when it is stripped from the form.

Another object is to provide a slab casting form that constitutes a unitary structure capable of withstanding prestressing loads and which may be prepared for casting simply by pivoting the side forms into casting position and latching them.

Another object is to provide a slab casting form in which the bottom element is of one piece construction with upturned edges and the side form elements fit down Patented Sept. 7, 1965 within the upturned edges in such a manner that leakage can occur only in the upward direction between them.

Another object is to provide a slab casting form in which the side forms pivot upwardly and outwardly when the slab is lifted thereby shearing off any upwardly projecting leakage flange that may have formed on the cast slab.

According to this invention, the casting of prestressed concrete slabs for floors and roofs or like structural elements is effected expeditiously with a minimum of hand labor. To this end, an improved slab casting form is constituted by a one piece bottom element having upturned edges adapted to mold the lower or ceiling portion of the slab with a continuous smooth surface. This bottom element is mounted in a rugged frame or cradle structure formed by spaced longitudinally disposed members of sufficient strength to sustain the reaction of the prestressing tension forces. The side form elements which are shaped to mold the sides of the slab and the indented grout keyway grooves along the edges of the slab are permanently hinged to the frame in manner to fit down tightly inside of the upturned edges of the bottom element. With this arrangement, any leakage or seepage of grout that may occur during casting of the slab is necessarily in the upward direction between these overlapping elements. After the slab has solidified, it may be lifted directly upward whereupon the hinged side forms pivot upwardly and outwardly automatically to permit the slab to be stripped out of the bottom element and to move upward between the pivoting side elements. As this occurs, any grout flange that may have formed through seepage is sheared off by the outwardly pivoting side form. The side form hinges are provided with lost motion slot-s arranged to permit outward sliding of the side forms in clearing the slab to obviate any cramping of the slab between the side forms as it is being lifted.

The foregoing and other objects of this invention will become more readily apparent upon perusing the following detailed description of embodying apparatus in conjunction with the accompanying drawing showing an improved slab casting mold illustrative of the invention in its presently preferred form wherein:

FIGURE 1 is a view in perspective of concrete slab casting forms embodying the invention arranged in endto-end abutting relationship, the form in the foreground being illustrated in closed position ready to receive plastic concrete while the form shown fragmentarily in the background is in open position;

FIG. 2 is a fragmentary view in perspective and partly in transverse section illustrating a floor structure formed by juxtaposed precast floor slabs of the type molded in the forms shown in FIGURE 1;

FIG. 3 is an enlarged view in transverse section through the slab casting form taken along the plane represented by the line 3-3 in FIGURE 1 and also through a slab that has been cast therein;

FIG. 4 is a view in transverse section generally similar to PEG. 3 but taken through the form along the plane represented by the line 4-4 in FIGURE 1 and also showing in section a finished slab partially lifted from the form;

FIG. 5 is an enlarged fragmentary view in transverse section through the left side of the form structure as generally shown in FIGS. 1, 3 and 4 with tilted positions of the side form indicated by broken lines and also illustrating a modification constituting a side form extension; and,

FIG. 6 is a fragmentary plan view of part of the right side of the form with parts broken away to show the side form locking arrangement.

The drawing illustrates improved arrangements for the manufacturing of flat structural elements such as precast concrete Slabs utilized for floors and roofs in building construction and the like and that are made in various lengths, widths and thicknesses to suit the circumstances of their use. The particular casting form shown in the drawing by way of illustration is adapted to mold prestressed slabs S of the type illustrated in perspective in FIG. 2. As there shown in a representative structure, a series of typical slabs S made in the illustrated forms may be laid side by side to span suitable supporting beams or the like for forming the floor of a room, for example, the smooth lower surfaces of the slabs at the same time forming the ceiling of the room below. As shown in the drawing, the floor presents a unified surface in which adjacent slabs S are locked together in a manner to transmit shear stresses from one to another by means of interposed grout keys thereby forming a continuous integral platform structure.

The grout keys 10 are cast in place by introducing grout in plastic condition into grout canals or keyways 11 formed between the contiguous edges of adjacent slabs when the slabs are laid in juxtaposed position as shown in FIG. 2.. The interposed keying channels or keyways 11 are formed by complementary longitudinally extending re-entrant grooves 12 indented into the upper parts of the respective edges of the slabs S during casting, the slabs being in contact with each other only along a line at the lower border of each of the keyways 11 whereby each keyway is closed at the bottom to retain the plastic grout when it is poured between the slabs. After the grout has set, each key 10 so formed constitutes a rigid load transferring and interlocking groove filling element between adjacent slabs.

As shown in the drawing, each slab S is provided with a plurality of relatively large cylindrical cored openings 13 extending in spaced parallel relationship from end-toend within the slab and constituting voids that serve to lighten the structure. Ordinarily these voids constitute from forty to fifty percent of the volume of the slab. Beneath the parallel passages 13, a plurality of longitudinal reinforcing strands in the form of rods or wires 15 are arranged lengthwise within the slab near its lower surface. These reinforcing strand elements 15 are ordinarily prestressed in well-known manner during casting of the slab in order to increase the load carrying efliciency of the structure. The lower side of the floor slab S that constitutes the ceiling of the room below, preferably presents a continuous smooth surface that is attractive in appearance.

The slabs S of FIG. 2 are of the type cast individually in improved steel forms shown in perspective in FIG- URE 1, several forms being ordinarily arranged in endto-end abutting relationship as indicated in order that a number of slabs may be cast in the same operation thereby simplifying the procedure and reducing the cost. The particular form 20 illustrated in the drawing is adapted to cast slabs S that are eight inches thick and four feet wide and that are formed in lengths suitable to the structure being built.

Although only one style of casting form is shown in the drawing, it is to be understood that the forms 2-0 may be made in any other sizes and proportions that may be suitable for casting slabs and the like in the different dimensions and shapes required under various circumstances. The improved form 29 to which this invention is directed is made self-releasing to permit ready removal of the slab S cast in it, the form in the foreground in FIGURE 1 being in closed position for receiving the plastic concrete while the form shown fragmentarily in the background is in open position as it would be after having released a slab cast therein.

Referring now more specifically to the drawing and particularly to FIGURE 1 thereof, each of the slab casting forms 20 comprises essentially a main framework 21 that is in the general shape of a form holding cradle and that encloses and supports a bottom pan or form element 2. The pan 22 constitutes the lower or main part of the slab form or mold that shapes the smooth lower surface of the slab S. The indented upper or side edge parts 12 of the slab S are formed by a pair of movable, inwardly projecting side rail elements 23 that extend upwardly from and are hingedly mounted permanently on the respective sides of the framework 21 for upward and outward pivoting movement in releasing a slab that has been cast in the form. As may be seen in the drawing, the casting form 20 is allochiral or symmetrical about its longitudinal center line, the two side rails 23 and likewise the respective sides of the framework 21 being of similar construction but reversed in position.

The main framework 21 of each form 20 includes a pair of spaced parallel heavy rigid side members or longitudinal beams 24 that are shown as being wide-flange I-beams and are of sufficient strength to withstand the compressive reactions of the prestressing forces applied to the reinforcing strand elements 15 during casting of the slabs. Although shown as I-beams, the stressing side members 24 may be formed instead by channel box sections or by any other suitable structural members capable of sustaining the compressive stresses resulting from the pretensioning operation. As shown, each I-beam side member 24 is provided at each end with a pressure pad 25 constitute-cl by a rectangular steel plate that is welded to and covers the end of the beam whereby a series of successive forms 20 may be abutted end-to-end as inidicated in FIGURE 1 and stressed as a unit.

The two heavy side members 24 are interconnected at their lower edges and positioned in parallel relationship by a plurality of spaced lateral supporting members or transverse members 26 that are shown as constituted by inverted channel elements resting upon and welded at their respective ends to the lower flanges of the I-bearns 24. These cross or lateral channel members 26 are preferably spaced at regular intervals, usually about twenty inches apart, along the beams 24 to constitute the bottom of the unitary frame or cradle structure 21.

The bottom pan 22 is fitted within the cradle structure of the frame 21 between the side elements 24 and rests upon the spaced cross members 26. As shown, the pan 22 is formed in one piece from a unitary sheet of steel preferably about one-fourth inch thick that is turned up at its respective edges to constitute lower side wall elements 27. The upturned side walls 27 are blended to the bottom of the imperforate pan 22 by smoothly curved rounded fillets 28 to form a unitary trough-shaped or U-shaped bottom form that molds the lower side of the slab S as one continuous smooth surface. Since the pan 22 is of one piece without joints and therefore free from leakage, there is no possibility of seepage of grout from it which might otherwise result in marring the surface by leaving aggregates exposed or by forming protruding rough flanges.

The bottom pan 22 is supported upon the spaced cross members 26 within the cradle 21 with its upturned side walls 27 extending slightly above the tops of the respective beams 24, the upper edges of the side walls being welded to the edges of the beam flanges by longitudinally disposed weld seams. These upwardly turned side walls 27 mold the lower parts of the sides of the slab S up to the position at which the line contact is effected between adjacent slabs at the bottom of the keyway 11, the lower side walls of the slab being flared outwardly in order to insure that contact occurs between the adjacent slabs only along a line at the bottom of each of the keyways. Because of the outward flaring or batter of the side walls 27, the slab S when solidified in the form may be removed readily from the bottom pan 22 simply by drawing it directly upward.

As previously indicated, in order to form the idented longitudinal grooves 12 in the sides of the slab S above the line contact position to constitute the grout keyways or channels 11, it is necessary that the upper part of the form that molds the upper portion of the slab sides be recntrant and project inwardly beyond the side walls 27 to indent or undercut the slab sides. This requires then that these upper parts of the form be made movable in some manner to permit removal thereof for releasing the slab S after it has been cast therein. In accordance with a feature of this invention, side forms or plates 31 that are shaped to mold the grooves 12 in the upper parts of the slab sides are made movable though being formed as the innermost parts of the previously mentioned movable side rails 23 that are hingedly attached to the side beams 24.

As may best be seen in cross section in FIG. 3, the side plates 31 are set inwardly with respect to the side walls 27 of the bottom pan 22 and flare outwardly somewhat at their upper edges to mold the tapered sides 12 of the keyway groove 11. The lower edges of the side plates 31 are reverted or turned outwardly at right angles to mold the bottom of the keyway and they fit downwardly within and substantially flush with the top edges of the pan side Walls 27. By this arrangement, the side plates 31 operate to mold the indented longitudinal grooves 12 in the respective sides of the slab S that form the grout keyways 11 and that constitute upward extensions of the slab side walls. The upper or top edges of the side plates 31 constitute screed lines that serve to guide a straight edge or screed (not shown) in striking off the top surface of plastic concrete in the mold when forming the slab. With several forms arranged end-to-end, a single screed element may be operated along the entire group of forms to strike off all of the slabs at one time.

The lower outwardly turned edge of each side plate 31 is preferably closed fitted to the inside of the corresponding pan side wall 2'7 in manner to minimize the possibility of leakage at the joint between these two overlapping parts. By this arrangement any leakage that may occur must take place above the line contact juncture between adjacent finished slabs and furthermore it must occur in the upward direction and therefore tends to be limited.

Each side plate 31 of the mold form is supported in the side rail structure 23 and reinforced by a generally horizontal continuous top plate 34 that is welded to and extends longitudinally of the side plate and that projects outwardly from the top edge thereof just below its screed line surface. As best shown in FIGS. 3 and 5, the outer part of the horizontal top plate 34 is inclined downwardly and its outer edge is bent downward to form a vertical flange. The top plate 34 not only reinforces the molding side plate 31 but also extends outwardly over the corresponding side member 24 of the frame thereby forming a cover protecting the apparatus beneath it from contamination by plastic concrete that may be spilled over the sides of the form while molding the slab.

Vertically disposed outwardly extending stiffening plates are fitted at their inner ends to the outer sides of the side plates 31 and at their tops to the lower surfaces of the top or cover plates 34- to reinforce the side rail structure 23. As indicated in FIGURE 1, a stiffening plate 33 is provided near each end of each side rail 23 with an additional plate 35 placed midway between them.

Intermediate the stlfiening plates 35, hinge plates 36 are provided, these plates being spaced inwardly from each end about one-fourth the length of the side rail 23. The hinge plates 36 are generally similar in shape to the stificning plates 35 and perform the same reinforcing function but include in addition at their outer ends downwardly projecting hinge lugs 37. Each depending hinge lug 37 is provided with a horizontally disposed hinge slot 38 that slidably receives a hinge pin 39 carried by the frame side member 24.

As may best be seen in FIG. 6, each hinge plate 36 is so arranged and positioned that its depending hinge lug 37 fits downwardly between a pair of outwardly projecting closely spaced angle iron brackets 41 and 42 that are welded to the underside of the upper flange of the adjacent I-bcam 24. The hinge pin 39 which extends horizontally through the slot 38 in the hinge lug 37 also passes through and is secured at its respective ends in the two angle brackets 41 and 42 that straddle the sides of the hinge lug 37. By this arrangement, the entire side form member 23 including the inner slab molding side plate 31, the top plate 34 and the stiffening members 35 and 36 may be pivoted upwardly and outwardly as indicated in FIGURES 1, 4 and 5 about the pivot pins 33 and also may be translated laterally outward by sliding the hinge slots 38 over the pins 39.

Since the hinge pins 33 and their supporting brackets 4-1 and 42 are positioned below the top flanges of the side beams 24, the pivot pins 39 are disposed below the lower edges of the side plates 31 and therefore when the side rails 23 are pivoted upwardly about the pin axes as centers in lifting with the slab all parts of the side plates 31 also move outwardly in manner to free the plates from the sides of the slab S without interference, as indicated in FIGS. 4 and 5 thereby providing for automatic stripping of the slab. Furthermore, the horizontal slots 38 in the hinge lugs 37 are arranged to provide for outward sliding movement of the side rails 23, the outer ends of the slots 38 being positioned to prevent any further inward movement of the side plates 31 beyond the positions at which they cooperate with the side walls 27 of the pan 22 in constituting the complete slab mold. When the side plates 31 are pivoted upwardly, however, to release them from engagement with the pan side walls, the slots 38 provide lost-motion linkages or connections that permit further outward translatory movement of the side rails 23 as soon as their lower edges are lifted above the top edges of the pan side walls, as indicated in broken lines in FIG. 5 thereby obviating any possibility of cramping or other interference with the slab S as it is being lifted from the form.

As best shown in FIG. 5, both the stiffening plates 35 and the hinge plate 3-5 are relieved by notches 43 at their inner lower corners to provide clearance for the upper edges of the pan side walls 27. Accordingly, when the side rails 23 are in the closed or casting position, the lower horizontal edges of the plates 35 and 36 seat upon the upper flanges of the side element I-beams 24 rather than upon the tops of the pan edges.

In order to hold the side rails 23 down in operating position and to prevent them from moving upward or floating because of hydrostatic pressure when the plastic concrete is poured into the mold and vibrated, there is provided adjacent to each hinge plate 36 a pin locking or latching device 4 including a pin or bolt 45. As shown, the bolt 45 is slidably and rotatably mounted in aligned holes through an inverted U-shaped bracket 46 that is Welded at its ends to and is upstanding from the top flange of the side beam 24. The inner end of the locking bolt 4-5 is somewhat pointed to facilitate engagement with a complementary locking hole in a latching bracket 47 that projects outwardly from and is welded to the side of the hinge plate 36 near the side form 33.. The outer end of the locking bolt 45 is bent down at right angles to provide an operating handle. When the side rail 23 is in its lower or casting position as shown in full lines in FIG. 5, the bolt 45 may be pushed inwardly to engage its inner end with the cooperating hole in the bracket 47 thereby retaining the side rail in that position.

In order to insure that the locking bolt will remain in locked position, there is welded to one side of it within the bracket 46 a latching lug or keeper 43 that may be turned downward by rotating the bolt 45 to engage inwardly of a similar stationary cooperating lug or block 49 welded to the top of the side beam flange as shown in FIG. 5. Since the latching lug 48 secured to the bolt 45' is positioned within the U-shaped bracket 46 it serves also to retain the bolt in the bracket by limiting the extent to which it may be drawn outwardly. As shown in FIGS. and 6, the cooperating latch members 48' and 49 for the bolt 45 are both housed within and protected beneath the U-shaped bracket 46. Furthermore, the entire pin lock device 44 is placed closely adjacent to the hinge plate 36 and is housed beneath the top plate 34 whereby it is protected from spilled concrete or from any other damage that might otherwise be suffered if the locking device 44 were in an exposed position.

When it is decided to unlock the side rails, an operator may reach beneath the top plate 34- from the outer side of the form and turn each bolt 45, by means of its bent handle, through a quarter turn to disengage the latch block or lug 48 on the bolt 45 from the cooperating block 49 on the side beam 24. The bolt 45 may then be pulled outward to withdraw its inner end from the hole in the bracket 47 on the hinge plate 36. With all of the locking bolts 45 thus withdrawn, the side rails 23 are free to swing upwardly and outwardly about the pivot pins 39.

When preparing the form for casting, the side rails 23 are turned down and moved inwardly to engage the out-turned lower edges of the side plates 31 down within or inside of the upper edges of the pan side walls 27 respectively, as shown in FIGS. 3 and 5. All of the locking bolts 45 are then pushed inwardly and latched as shown in the drawing with their pointed inner ends engaged in the holes of the brackets 47 on the hinge plates 36 thereby preventing any upward movement of the side plates 31 during casting of the slab which might otherwise occur through hydrostatic pressure exerted by the plastic concrete when poured and vibrated as hereinbefore explained.

The slab casting process may then proceed in the usual well-known manner employed with formsof the prior art type now in general use. This involves closing the ends of the forms by means of end plates or bulkheads 51 that also constitute headers or divider plates between adjacent forms 20 when several slabs are being cast simultaneously end-to-end. The reinforcing rods or cables are then placed in position longitudinally of the several forms near the bottom of the pans 22 whereupon the strands are stressed to effect the desired prestressing tension in them.

In this prestressing process, the reaction of the forces applied to stress the strands is taken by the end pieces or pads 25 on the beams 24 and is transmitted as compressive stresses through the aligned beams 24 and from ,one beam to another throughout the series of forms that are arranged end-to-end with adjacent pressure pads 25 abutting each other and preferably bolted together as suggested in FIGURE 1. This predetermined tension is maintained in the strands 15 during casting of the slab and until the concrete has solidified. Inflatable tubes or other suitable cores for forming the longitudinal passages or voids 13 are then supported within the forms in the usual manner after which the freshly mixed concrete material in plastic condition is poured into the forms. The con crete may then be vibrated to insure'that air is displaced and that all parts of the forms are filled properly Whereupon the upper surface of the series of slabs is struck off by running a screed along the top edges of the side plates 31 as previously mentioned.

During the casting process, any leakage of fluid material or grout that may occur between the upturned side walls 27 of the pan 22 and the interfitting side plates 31 will necessarily be in upward direction and will form an upstanding thin grout flange or ragged edge when hardened that would constitute an imperfection if left on the side of the slab. After the vibrating and screeding of the slabs has been completed, a lifting bail 53 is inserted in the plastic concrete at the top of each slab near each end thereof as shown in FIGS. 3 and 4 for use when the concrete has solidified in lifting the slab from the form and subsequently in transporting and placing it.

In the event that it is desired to cast in this form 20 a slab that is somewhat thicker than the slab S shown in FIGS. 3 and 4, the form 20 may be made deeper by adding a side rail extension 55 to each side rail 23 as shown in FIG. 5. As there shown, the side rail extension 55 is of generally angular shape with one leg extending vertically to form an upward extension of the side plate 31 and with the other leg extended horizontally along the top plate 34. The extension plate 55 is preferably removably fastened to the side rail 23 by means of slotted key bolts 56 that extend upward through aligned openings in the top plate 34 and in the horizontal portion of the extension plate, the bolts being secured by wedges or keys 57 that are driven into their slots. By this arrangement, side rail extensions 55 may be attached readily to both side rails and likewise may be detached easily, whereby slabs of various thicknesses may be cast in the same forms 24 simply by applying to the side rails appropriate side rail extensions 55 of proper height. These thicker slabs are struck otf by screeding along the tops of the vertical legs of the extensions 55 in the usual manner and are otherwise similarly produced.

After the concrete of a slab cast in the form 20 has become sufiiciently solidified, the strand tensioning forces are relieved and the locking bolts are given a quarter turn and then pulled outward to unlatch the side rails 23. The end plates 51 may then be removed together with the cores whereupon the reinforcing strands 15 are cut at the ends of the slabs to free them for stripping from the form. A lifting connection such as a crane cable 59 is then connected to each of the two lifting bails 53 at the respective ends of the slab S whereupon the pretensioned newly cast product may be lifted vertically out of the bottom pan 22 with the form opening automatically as both movable side rails 23 swing outwardly in the manner illustrated in FIG. 4.

When the slab S is lifted upward, the side rails 23 together with the extensions 55 if attached, move upward with it, pivoting upwardly and outwardly about the pivot pins 39. As previously mentioned and as indicated in section in FIGS. 4 and 5, the angularity of this outward pivoting or canting action draws the side plates 31 outwardly away from the sides of the slab while moving upwardly with it. This outward movement occurs as soon as the out-turned lower edges of the side plates are raised above the edges of the pan side walls 27. As the side plates 31 clear the pan edges they begin to pivot outward and in doing so shear otf whatever vertical grout flanges may have been formed as the result of any upward leakage between the pan side walls 27 and the lower edges of the side plates 31 thereby trimming the slab edge to a clean smooth surface. 'Because of the fact that the grout flanges are sheared ofi and the further fact that leakage or seepage cannot occur at any other place in the form, the slab S is withdrawn from the form as a completely finished product that does not require any hand trimming or patching in order to make it ready for the market.

Should the slab happen to swing sideways as it passes upward between the side rails during lifting or should it accidentally move downward after being partially lifted, the side rails 23 are free to move outwardly somewhat farther to provide adequate clearance for random movements as indicated in FIG. 5 by reason of the lost-motion slots 38 in the hinge lugs 37 that are now inclined in position and that cooperate with and slide upon the pivot pins 39. This lost-motion connection prevents any cramping or keystoning action which might occur if the slab should move downward from a partially lifted position and that could otherwise result in wedging and damage to the side plates 31 or to other parts of the form structure.

After the newly cast slab S has been completely removed from the form 20, the pivotally connected side rails 23 tend to drop back into casting position and it is only necessary to see that the side plates 31 are clean and fit down properly within the side walls 27 and then lock them by means of the locking bolts 45 in order to prepare the form for receiving another batch of freshly mixed concrete. The form 20 is accordingly substantially self-closing in that no separate parts need to be replaced and no tools are required to reset it in condition to cast another slab after a previously cast slab has been removed by lifting it upward out of the bottom pan 22.

From the foregoing explanation of the invention and description of an exemplary flat slab casting form apparatus set forth herein, it will be apparent that there has been provided by the present invention a new and improved apparatus for forming floor slabs and similar structural elements from concrete or the like. As explained hereinbefore, the improvement in casting slabs and like members is accomplished by means of a new and novel self-releasing and self-closing steel form apparatus that may be operated with a minimum of hand work to produce cast concrete slabs of superior quality and that does not involve loose parts to be removed and replaced nor require the use of tools in manipulating the form during the casting operation.

Although only one size and style of the improved slab casting form has been shown and described in detail herein as a specific example illustrative of a practical working embodiment of the invention by way of a full disclosure, it is to be understood that the novel features of this self-releasing slab form may be utilized by those skilled in the art of casting concrete structural elements in various other forms which though differing in shape and material nevertheless come within the spirit and scope of the invention as defined in the following claims.

The invention having now been fully described and explained, I claim as my invention:

1. In a slab casting form for molding flat slabs of concrete such as are used in building construction and the like, a frame constituting a mold cradle, a mold pan of sheet metal having upturned edges mounted horizontally in said cradle and adapted to mold the bottom and sides of the lower art of a slab being cast therein, side forms of sheet metal interfitting within said upturned edge of said pan and extending upwardly therefrom to mold the sides of the upper part of a slab being cast therein, a plurality of vertically disposed sheet metal hinge plates secured to and extending outwardly from each of said upwardly extending side forms, said hinge plates being provided at their outer lower edges with horizontally disposed slots, hinge pins carried by said frame and disposed to slidably engage said slots in said hinge plates in manner to provide lost motion hinges for upward and outward pivoting movement of said side form and for outward translatory movement thereof in releasing a slab cast in said form, manually actuated locking bolts slidably mounted on said frame adjacent to said hinge lates, latches secured to said hinge plates in position to be engaged by said locking bolts when said side form is in casting position, and a continuous sheet metal cover plate extending from said side form outwardly over said hinge plates in manner to cover and protect said hinges and said locking bolts, said cover plate being secured to both said side form and said hinge plates to constitute therewith a reinforced structure adapted to obviate distortion of said side form, the arrangement being such that when a slab cast in said form has solidified said locking bolts may be disengaged from said latches whereupon said side forms are free to move upward with the slab as it is lifted from said mold pan and also to move outwardly from the sides of the slab to provide clearance for removal of the slab from the form.

2. In forms adapted for abutting end-to-end in casting prestressed concrete slabs, each form comprising spaced longitudinally disposed side frame members adapted to sustain the reaction of prestressing forces, pressure pads on each end of each side frame member for abutting an adjacent form and receiving prestressing forces therefrom, transverse members interconnecting said side frame members to form a cradle structure, a one-piece form pan of sheet material turned up at its longitudinal edges and fitted within said cradle structure between said side frame members, a side rail structure movably mounted on each of said side frame members, lost-motion hinges interconnecting said side rail structures respectively to said side members in a manner to provide for upward and outward pivoting movement of said side rails and for limited outward translatory movement thereof relative to their associated side members, side forms constituting the inner faces of said movable side rail structures and adapted to extend inwardly of and to fit down within the upturned longitudinal edges of said form pan the space therebetween presenting a vertical leakage path, and latches releasably securing said side rails to said side member with said side forms disposed in cooperating relationship with said form pan to constitute a slab form, the arrangement being such that after a concrete slab cast in said form has solidified said latches may be released and the slab then lifted upwardly from said form an with said side rails pivoting upwardly and outwardly and sliding outwardly to clear the slab as it is lifted from said form and with said side forms in moving outwardly shearing off any leakage flanges that may have been formed in said vertical leakage paths.

3. In a mold form for casting flat prefabricated slabs of concrete for use in building construction, a frame constituting a supporting cradle, a mold pan having upturned edges mounted horizontally in said cradle and adapted to mold the lower part of a slab being cast therein, movable side forms disposed to cooperate with said pan to mold the sides of the slab being cast, said side forms fitting within said upturned edges of said pan, and lost-motion hinges operatively connecting said side forms to said cradle in manner to provide for upward and outward ivoting movement of said side forms relative to said pan.

4. In a form for molding flat slabs of concrete and the like, a frame constituting a mold cradle, a mold pan having upturned sides mounted in said cradle and adapted to mold the lower part of a slab being cast therein, a movable side form interfitting with each upturned side of said mold pan and extending upwardly therefrom to mold the sides of the upper part of a slab being cast therein, a side form locking device for each side form including an inverted U-shaped bracket presenting aligned holes and mounted on said frame transversely of but outwardly from said mold pan, a locking bolt slidably mounted in said aligned holes of each bracket for movement toward or from said corresponding side form, a latching bracket carried by said side form in position to releasably receive said locking bolt, a keeper secured to said bolt within and protected by said U-shaped bracket, said keeper serving to retain said bolt in said bracket while permitting endwise locking movement thereof, a lug on said frame positioned and arranged to be engaged by said keeper upon turning said bolt to retain it in locking engagement with said latching bracket on said side form said lug also being within and protected by said inverted U-shaped bracket, and a cover plate extending longitudinally of and horizontally outward from each of said side forms in manner to reinforce said side form and to cover and protect said side form locking devices.

5. In a slab casting form for molding concrete building slabs of the type presenting indented sides constituting keying channels, an imperforate lower form element having upturned side edges and shaped to mold the bottom and the lower side edges of a building slab, movable reentrant side forms superimposed upon and interfitting with the respective upturned side edges of said lower form element in a manner to fit down inwardly of and to overlap the tops of said upturned side edges said side forms being shaped to mold the indented keying channels in the upper side edges of the slab, and connecting means including lost motion linkages movably interconnecting said reentrant side forms and said lower form element in a manner providing for limited upward and outward movement of said side forms relative to said lower form element.

References Cited by the Examiner UNITED STATES PATENTS 2,075,607 3/37 Griesel 25--121 2,306,107 12/42 Henderson 25121 2,366,656 1/45 SafiFert 25l 18 12 2,739,365 3/56 Choquette 264-256 2,740,162 4/56 Knight 264-256 2,758,353 8/56 Carlson et al 25121 2,779,080 1/57 Chidester 25-120 2,823,440 2/58 Schade 25121 2,886,876 5/59 Wilson 25121 2,892,339 6/59 Flower et a1 25121 3,116,530 1/64 Francis 25-118 10 WILLIAM J. STEPHENSON, Primary Examiner;

ALEXANDER H. BRODMERKEL, MICHAEL V.

BRINDISI, Examiners. 

1. IN A SLAB CASTING FORM FOR MOLDING FLAT SLABS OF CONCRETE SUCH AS ARE USED IN BUILDING CONSTRUCTION AND THE LIKE, A FRAME CONSTITUTING A MOLD CRADLE, A MOLD PAN OF SHEET METAL HAVING UPTURNED EDGES MOUNTED HORIZONTALLY IN SAID CRADLE AND ADAPTED TOI MOLD THE BOTTOM AND SIDES OF THE LOWER PART OF A SLAB BEING CASTING THEREIN, SIDE FORMS OF SHEET METAL INTERFITTING WITHIN SAID UPTURNED EDGES OF SAID PAN AND EXTENDING UPWARDLY THEREFROM TO MOLD THE SIDES OF THE UPPER PART OF A SLAB BEING CAST THEREIN, A PLURALITY OF VERTICALLY DISPOSED SHEET METAL HINGE PLATES SECURED TO AND EXTENDING OUTWARDLY FROM EACH OF SAID UPWARDLY EXTENDING SIDE FORMS, SAID HINGE PLATES BEINE PROVIDED AT THEIR OUTER LOWER EDGES WITH HORIZONTALLY DISPOSED SLOTS, HINGE PINS CARRIED BY SAID FRAME AND DISPOSED TO SLIDABLY ENGAGE SAID SLOTS IN SAID HINGE PLATES IN MANNER TO PROVIDE LOST MOTION HINGES FOR UPWARD AND OUTWARD PIVOTING MOVEMENT OF SAID SIDE FORM AND FOR OUTWARD TRANSLATORY MOVEMENT THERETO IN RELEASING A SLAB CAST IN SAID FORM, MANUALLY ACTUATED LOCKING BOLTS SLIDABLY MOUNTED ON SAID FRAME ADJACENT TO SAID HINGE PLATES, LATCHES SECURED TO SAID HINGE PLATES IN POSITION TO BE ENGAGED BY SAID LOCKING BOLTS WHEN SAID SIDE FORM IS IN CASTING POSITION, AND A CONTINUOUS SHEET METAL COVER PLATE EXTENDING FROM SAID SIDE FROM OUTWARDLY OVER SAID HINGE PLATES IN MANNER TO COVER PLATE BEING SECURED TO BOTH SAID SIDE BOLTS, SAID COVER PLATE BEING SECURED TO BOTH SAID SIDE FORM AND SAID HINGE PLATES TO CONSTITUTE THEREWITH A REINFORCED STRUCTURE ADAPTED TO OBVIATE DISTORTION OF SAID SAID FORM, THE ARRANGEMENT BEING SUCH THAT WHEN A SLAB CAST IN SAID FORM HAS SOLIDIFIED SAID LOCKING BOLTS MAY BE DISENGAGED FROM SAID LATCHES WHEREUPON SAID SIDE FORMS ARE FREE TO MOVE UPWARD WITH THE SLAB AS IT IS LIFTED FROM SAID MOLD PAN AND ALSO TO MOVE OUTWARDLY FROM THE SIDES OF THE SLAB TO PROVIDE CLEARANCE FOR REMOVAL OF THE SLAB FROM THE FORM. 